Lactoferrin is a single chain metal binding glycoprotein. Many cell types, such as monocytes, macrophages, lymphocytes, and brush-border cells in the intestine, are known to have lactoferrin receptors. Lactoferrin is found mainly in external secretions of mucosal epithelia such as breast milk, saliva, tears, bile, and pancreatic fluid and has a wide array of functions related to host primary defense mechanisms. For example, lactoferrin has been reported to activate natural killer (NK) cells, induce colony stimulating activity, activate polymorphonuclear neutrophils (PMN), regulate granulopoeisis, enhance antibody-dependent cell cytotoxicity, stimulate lymphokine-activated killer (LAK) cell activity, and potentiate macrophage toxicity. Lactoferrins have been reported to have a number of beneficial effects including anti-infective, anti-inflammatory, immunomodulatory and anti-cancer activities.
Recombinant human lactoferrin has previously been described as being purified after expression in a variety of prokaryotic and eukaryotic organisms including aspergillus (U.S. Pat. No. 6,080,559), cattle (U.S. Pat. No. 5,919,913), rice, corn, Sacharomcyes (U.S. Pat. No. 6,228,614) and Pichia pastoris (U.S. Pat. Nos. 6,455,687, 6,277,817, 6,066,469). Also described are expression systems for the expression of full-length human lactoferrins (e.g. U.S. Pat. No. 6,100,054). In all cases, part of the teaching is expression of the full length cDNA and purification of the intact protein whose N-terminal, after processing of the leader peptide, is the amino acid glycine. Nuijens, et al. (U.S. Pat. No. 6,333,311) separately describe variants of human lactoferrin but their focus is limited to deletion or substitution of arginine residues found in the N-terminal domain of lactoferrin.
LF contains a strongly basic region close to its N-terminus and binds to a variety of anionic biological molecules including lipid A (Appelmelk et al., Infect. Immun. 62:2628-2632 (1994)) and glycosaminoglycans which occur on the surface of most cells and in most extracellular matrices (Mann et al., J. Biol. Chem. 269: 23661-7 (1994)). Lactoferricin H (residues 1-47) and lactoferricin B (residue 17-41) are released by pepsinolysis of human or bovine LF, respectively, and may have more potent antibacterial activity than the native proteins (Bellamy et al., Biochim. Biophys. Acta. 1121: 130-136 (1992)). A region composed of residues 28-34 is reported to contribute to the high affinity binding of human LF and lactoferricin H to endotoxin (Elass-Rochard et al., Biochem. J. 312: 839-845 (1995)). LF and lactoferricin B have been shown to inhibit the endotoxin-induced interleukin-6 response in human monocytic cells (Mattsby-Baltzer et al., Pediatr. Res. 40: 257-262 (1996)). Previously identified fragments of LF which exhibit antimicrobial activity were isolated from pepsin hydrolysates of LF (Tomita et al., (1993) U.S. Pat. No. 5,214,028; Tomita et al., (1994) U.S. Pat. No. 5,304,633; Tomita et al., (1994) U.S. Pat. No. 5,317,084; Tomita et al., (1997) U.S. Pat. No. 5,656,591).
Previous studies have established that the N-terminal 33 residues of human LF represent the minimal sequence that mediates binding of the protein to anionic polysaccharides such as glycosaminoglycans (Mann et al., J. Biol. Chem. 269: 23661-7 (1994)). This sequence contains a cationic head (residues 1-6) and tail (residues 28-33) which combine to form the glycosaminoglycan-binding site. In further studies described by Mann in U.S. Pat. No. 6,399,570, lactoferrin peptide fragments having up to the first 51 amino acids encompassed endotoxin neutralizing ability and antimicrobial activity. Mann further showed that up to 17 amino acids could be deleted from the C-terminus and up to 3 amino acids could be deleted N-terminus of the 51 amino acid long peptide while retaining the endotoxin neutralizing ability and antimicrobial activity.
The present invention is the first to describe a peptide composition that consists of lactoferrin related peptides which are at least 33 amino acids in length in which at least four amino acids at the C and/or N terminus are substituted for positive amino acids resulting in an enhancement of its biological activity.